The Chandra High Resolution X-ray Spectrum of Quiescent Emission from Sgr A*. (arXiv:2002.07198v1 [astro-ph.HE])

The Chandra High Resolution X-ray Spectrum of Quiescent Emission from Sgr A*. (arXiv:2002.07198v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Corrales_L/0/1/0/all/0/1">L. Corrales</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baganoff_F/0/1/0/all/0/1">F. K. Baganoff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_Q/0/1/0/all/0/1">Q. D. Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nowak_M/0/1/0/all/0/1">M. Nowak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neilsen_J/0/1/0/all/0/1">J. Neilsen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Markoff_S/0/1/0/all/0/1">S. Markoff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haggard_D/0/1/0/all/0/1">D. Haggard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Davis_J/0/1/0/all/0/1">J. Davis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Houck_J/0/1/0/all/0/1">J. Houck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Principe_D/0/1/0/all/0/1">D. Principe</a>

In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than
expected for its environment. This problem has motivated a host of theoretical
models to explain radiatively inefficient accretion flows (RIAFs). The Chandra
Galactic Center (GC) X-ray Visionary Program obtained approximately 3 Ms (one
month) of Chandra HETG data, offering the only opportunity to examine the
quiescent X-ray emission of Sgr A* with high resolution spectroscopy. Utilizing
custom background regions and filters for removing overlapping point sources,
this work provides the first ever look at stacked HETG spectra of Sgr A*. We
model the background datasets with a cubic spline and fit the unbinned Sgr A*
spectra with a simple parametric model of a power law plus Gaussian lines under
the effects of interstellar extinction. We detect a strong 6.7 keV iron
emission line in the HEG spectra and a 3.1 keV emission line in the MEG
spectra. In all cases, the line centroids and equivalent widths are consistent
with those measured from low-resolution CCD spectra. An examination of the
unbinned, stacked HEG+/-1 spectrum reveals fine structure in the iron line
complex. In addition to resolving the resonant and forbidden lines from He-like
iron, there are apparent emission features arising with higher statistical
significance at lower energy, potentially associated with FeXX-XXIV ions in a
~1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we
release the cleaned and stacked Sgr A* and background HETG spectra to the
public as a special legacy dataset.

In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than
expected for its environment. This problem has motivated a host of theoretical
models to explain radiatively inefficient accretion flows (RIAFs). The Chandra
Galactic Center (GC) X-ray Visionary Program obtained approximately 3 Ms (one
month) of Chandra HETG data, offering the only opportunity to examine the
quiescent X-ray emission of Sgr A* with high resolution spectroscopy. Utilizing
custom background regions and filters for removing overlapping point sources,
this work provides the first ever look at stacked HETG spectra of Sgr A*. We
model the background datasets with a cubic spline and fit the unbinned Sgr A*
spectra with a simple parametric model of a power law plus Gaussian lines under
the effects of interstellar extinction. We detect a strong 6.7 keV iron
emission line in the HEG spectra and a 3.1 keV emission line in the MEG
spectra. In all cases, the line centroids and equivalent widths are consistent
with those measured from low-resolution CCD spectra. An examination of the
unbinned, stacked HEG+/-1 spectrum reveals fine structure in the iron line
complex. In addition to resolving the resonant and forbidden lines from He-like
iron, there are apparent emission features arising with higher statistical
significance at lower energy, potentially associated with FeXX-XXIV ions in a
~1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we
release the cleaned and stacked Sgr A* and background HETG spectra to the
public as a special legacy dataset.

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